Decreased expression of cholesterol 7alpha-hydroxylase and altered bile acid metabolism in Apobec-1-/- mice lead to increased gallstone susceptibility.

Abstract

Quantitative trait mapping in mice identified a susceptibility locus for gallstones (Lith6) spanning the Apobec-1 locus, the structural gene encoding the RNA-specific cytidine deaminase responsible for production of apolipoprotein B48 in mammalian small intestine and rodent liver. This observation prompted us to compare dietary gallstone susceptibility in Apobec-1(-/-) mice and congenic C57BL/6 wild type controls. When fed a lithogenic diet (LD) for 2 weeks, 90% Apobec-1(-/-) mice developed solid gallstones in comparison with 16% wild type controls. LD-fed Apobec-1(-/-) mice demonstrated increased biliary cholesterol secretion as well as increased cholesterol saturation and bile acid hydrophobicity indices. These changes occurred despite a relative decrease in cholesterol absorption in LD-fed Apobec-1(-/-) mice. Among the possible mechanisms to account for this phenotype, expression of Cyp7a1 mRNA and protein were significantly decreased in chow-fed Apobec-1(-/-) mice, decreasing further in LD-fed animals. Cyp7a1 transcription in hepatocyte nuclei, however, was unchanged in Apobec-1(-/-) mice, excluding transcriptional repression as a potential mechanism for decreased Cyp7a1 expression. We demonstrated that APOBEC-1 binds to AU-rich regions of the 3'-untranslated region of the Cyp7a1 transcript, containing the UUUN(A/U)U consensus motif, using both UV cross-linking to recombinant APOBEC-1 and in vivo RNA co-immunoprecipitation. In vivo Apobec-1-dependent modulation of Cyp7a1 expression was further confirmed following adenovirus-Apobec-1 administration to chow-fed Apobec-1(-/-) mice, which rescued Cyp7a1 gene expression. Taken together, the findings suggest that the AU-rich RNA binding-protein Apobec-1 mediates post-transcriptional regulation of murine Cyp7a1 expression and influences susceptibility to diet-induced gallstone formation.

• Authors: Yan Xie, Valerie Blanc, Thomas A Kerr, Susan Kennedy, Jianyang Luo, Elizabeth P Newberry, Nicholas O Davidson
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 284 Issue 25 Pg. 16860-16871 (Jun 19 2009) ISSN: 1083-351X [Electronic] United States
• PMID: 19386592 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• 3' Untranslated Regions
• Bile Acids and Salts
• RNA, Messenger
• Recombinant Proteins
• Cholesterol
• Cholesterol 7-alpha-Hydroxylase
• APOBEC-1 Deaminase
• Apobec1 protein, mouse
• Cytidine Deaminase

Topics

• 3' Untranslated Regions
• APOBEC-1 Deaminase
• Animals
• Animals, Genetically Modified
• Base Sequence
• Bile Acids and Salts (metabolism)
• Binding Sites (genetics)
• Cholesterol (metabolism)
• Cholesterol 7-alpha-Hydroxylase (genetics, metabolism)
• Cytidine Deaminase (deficiency, genetics, metabolism)
• Diet (adverse effects)
• Gallstones (etiology, genetics, metabolism, pathology)
• Hepatocytes (metabolism)
• Male
• Mice
• Mice, Congenic
• Mice, Inbred C57BL
• Mice, Knockout
• Phenotype
• RNA Processing, Post-Transcriptional
• RNA, Messenger (genetics, metabolism)
• Recombinant Proteins (genetics, metabolism)
• Transfection